Macrocytosis

An increased erythrocyte size defined by an elevated mean corpuscular volume (MCV >100 fL), reflecting enlargement of red blood cells due to impaired maturation, altered erythropoiesis, or increased production of larger immature erythrocytes.

Causes

• Nutritional causes: Malnutrition and/or malabsorption

  • Vitamin B12 deficiency

  • Folate deficiency

• Pernicious anemia --> Megaloblastic anemia due to impaired DNA synthesis

• Chronic alcohol use

• Liver disease

• Medications interfering with DNA synthesis or bone marrow function

  • HIV antiretroviral therapy

  • Chemotherapy agents

  • Antiseizure medications

• Hypothyroidism

• Myelodysplastic syndrome --> affecting erythrocyte production

• Hemorrhage --> Increased erythrocyte production

• Hemolysis causing compensatory erythropoiesis

• Pregnancy

• Chronic systemic illness

• Genetic disorders affecting red blood cell maturation